The present invention relates generally to an elastic bushing structure for use in a vehicle suspension system, and more particularly to such bushing structure which has provisions for restraining an increase in elastic yielding or deformation of a resilient member when radial or rotational loads to be applied to the structure exceed a given limit, thereby enhancing driving maneuverability and stability of the vehicle.
In a vehicle suspension system known in the art, various types of suspension members in the form of, for example, arms, rods and links are connected to parts of the vehicle chassis, axle housing and like members of the vehicle so that the suspension members are pivotable in various directions. To damp or absorb vibrations transmitted to those suspension members and for other purposes, a resilient suspension bushing has been commonly used for pivotal connections at both ends of each suspension member.
For example, there is shown in FIG. 1 a known 4-link wheel suspension system wherein a rigid axle housing 1 accommodating an axle is pivotally supported by a vehicle chassis through a pair of upper control arms 2 and a pair of lower control arms 3 which are disposed perpendicularly to the axle so that the axle housing 1 is vertically oscillatable. A bushing assembly 5 is incorporated in each of pivotal connections 4 between the ends of the control arms 2, 3, and the axle housing 1 and the chassis. Similarly, the bushing assembly 5 is used in pivotal connections at both ends of a lateral control rod 6 with the axle housing 1 and the chassis.
As shown in FIG. 2, the above indicated suspension bushing 5 comprises an inner cylindrical metal member 7 in which is inserted a suitable fulcrum shaft supported by a fixed member for suspension purpose, and further comprises an annular resilient member 8 secured to the outer periphery of the inner cylindrical metal member 7. This bushing assembly 5 of the inner member 7 and the resilient member 8 is adapted to be press-fitted in an outer cylindrical metal fitting or suspension arm eye 9 concentric with the inner and resilient members 7 and 8.
A damper or shock absorber including such suspension bushing assembly or structure 5 exhibits linear elastic or spring characteristics as represented by broken line A of FIG. 4, wherein the elastic deformation or strain of the resilient member in a direction normal to the axis thereof (in the radial direction R) is in substantially direct proportion to a load or stress applied to the structure 5 in the radial direction. This means that as the resiliency of the resilient member is reduced (the more soft material is used for the resilient member) the resilient member can absorb vibrations, noises, etc. with increased ease, but it is elastically deformed an increased amount with a result of degrading driving stability and maneuverability. The same relation exists between the magnitude of a rotational torque load applied to the structure in a direction T so as to cause the axis of the structure to be inclined, and the amount of elastic deformation produced by such torque load. Thus, the known suspension bushing structure has a drawback that it is incapable of assuring satisfactory driving maneuverability and stability while fulfilling its original function of vibration damping, and shock and noise absorption.